The conventional flush tanks used in toilets are designed to discharge a standard volume of water everytime these are flushed. Sometimes, however, the full discharge or flush is not necessary such that much water is actually wasted. In order therefore to reduce the volume of water used in flushing, various improvements were made on the flushing system of the flush tanks. One such improvement consists of a float operated cam for retaining the valve stem of a ball valve in a flush position until the float lowers to a preselected level, then releases the ball valve stem. This improvement allows the regulation of the flushing operation by limiting the quantity of water discharged from a water closet. In another improvement, selective flushing is effected by the use of valves at different elevations. By opening the valve located close to the water closet bottom a large volume of water is discharged for flushing. The more elevated valve is opened when a much lesser volume of water is needed for flushing.